Loud-speaker system



June 26, 1928.

1,675,031 F. A. KOLSTER LOUD SPEAKER SYSTEM Filed Sept. 1'7, 1925 FIE J(NI/EN Toe fiede/v'ck 14. ho/sfer:

Patented June 26, 1928.

UNITED STATES GRAPH COMPANY, FOB-KIA.

I 1,675,031 PATENT oFF cE.

FREDERICK A. KOLSTEB, or PALO ALTO, CALIFORNIA, assrenon To FEDERALTELEMor SAN EEAncIsoo, CALIFORNIA, A CORPORATION or can:-

- LOUD-SPEAKER SYSTEM.

Application filed September 17 1925. Serial No. 56.800. W

broadcast receivers for converting the de-,

tected and amplified radio energ into sound.

It is an object of this invention therefore to devise a' translatingsystem-which will translate electrical energy modulated at voicefrequencies into sound waves with substantially no distortion; that is,a system in which a translator will. give substantially the sameresponse for any frequency within the entire range of Voice frequencies.

It is a further object of this invention to devise such a system inwhich the voice frequency range is divided up into a plurality offrequency bands by means of a plurality of electrical units. It isproposed to allow each unit to translate its frequency band intomechanical vibrations.

Itis a further object of this invention to provide .a single aperiodicreproducer for' It is a further object of this invention to devise asystem which converts the electrical energy into mechanical vibrationsby means of a plurality of electricalunits and to im-' pose thesevibrations longitudinally upon a plurality of rods and to connect theserods to a common aperiodic diaphragm.

Further objects of the invention will appear from the followingdescription where I have disclosed the"preferred embodiments of myinvention. N

Referring to the drawings:

Figure 1 showsa loud speaker system applied to the output of avacuum-tube amplifier and constructed according to the principle of minvention.

Fig. 2 s ows sound response curves for the systemdisclosed' in Fig. 1.

Fig. 3 is an application of the system' shown in Fig. 1.

Fig. 4. is another modification of the systom shown in Fig, 1.

\Vhen electrical energy is modulated by means of the human voice orbyfmusic-the result is to produce a plurality 'of superposed electricalvibrations which range in frequency all the way from 50 to 10,000 cyclesper second. In the past loud speak- "crs have usually" been constructedwith' a single magnetic unit whiclrliad its pole pieces placed inproximity-tea; steel diaphragm. WVith such loudspeakers there are twodifferent inherent sources distortion. One is the natural resonanceof'the winding of the magnetic unitwhich is resonant at some pointwithin the'voice frequency range. The other is due to the naturalmechanical resonance of the diapliragm. If a sound response curve forsuch a loud speaker j is plotted between sound response and fre quenryfor a given energy input','it will be found that the curve will haveseveral,

humps or peaks which correspond to these resonant points. Thecurye'sLalsofall off rapidly for the lower-frequencies and for thehigher frequencies. .Therefore, such a loudspeaker will convertthelelectrical vibrations into sound at greater'efiiciency for certainfrequencies than for .fothers, thus producing distortion. i 1 I q i Ithas been found by experimentation that if a loud speaker will giveuniform response or faithful reproduction for frequencies ranging from50110 5000 cycles per second no appreciable distortion will be apparent.The system of this invention has therefore been designed to give a flattop characteristic response curve for frequencies ranging from 50 to5000 cycles per second. However. it should be underitood that the sameprinciples may be applied 'to produce a fiat top response curve forfrequencies ranging. up to as high as 10,000 cycles per second.

In that embodiment of the invention shown in Fig. 1 of the drawings thesystem is shown as applied to the out-put of :1 cascade vacuum tubeamplifier. This amplifier .is preferably of the standard impedance 13,electron emission element 14 and plate 15. The input circuit 16 of thevacuum 10 is suitably coupled to some source of electricalenergy'modulated at voice frequency and is connected to the grid 13 andelectron emission element 14 in the usual manner. In the output circuit17 of the'tube 10 there is an impedance. 18 having its upper terminalelectrically connected with the grid 13 of the vacuum tube 11 in serieswith the condenser 19. The usual grid leak 20 is connected between thegrid 13 of the vacuum tube 11 and the electron emission element 14 ofthis tube. The electron emission elements 14 of the vacuum tubes 10 and11 are. energized from a common A battery 21, and the output circuits 17and 12 of the two vacuum tubes are energized from a common B battery 22.

In the output circuit 12 of the vacuum tube 11 there is provided aplurality of electrical units, each of which converts a portion of theoutput energy into mechanical vibrations. These electrical units are sodesigned that they: 821th convert electrical energy into mechanicalvibrations most. efficiently at a certain point along the voicefrequency range, and these points are distributed along the voicefrequency range from 50 to 5000 cycles. Three of these electrical units125, 225 and 325 have been shown and they each preferably comprise atransformer or other coupling arrangement 26 having a primary winding 27and a sec ondary winding 28. The secondary 28 is connected to the magnetwindings 29 of a telephone unit which telephone unit also in the case oftheunit 125 includes a diaphragm 130. 'A capacitance 30 is connected inshunt with the windings '29. The inductance value of the windings.

29 and of the capacitances of the condensers 30 are so selected that theelectrical units will be resonant at some frequency within the voicerange and the arrangement is such that the resonant points are spacedthroughout the voice frequency range or at least from 50 to 5000 cyclesper second. To prevent the resonance peaks from being too sharplydefined a large amount of damping is introduced by making the windings29 of comparatively high resistance. To prevent the introduction ofdistortion due to the mechanical resonance of the diaphragms, it ispreferable to constructthe diaphragm for the telephone units whichtranslate the higher frequencies relatively. smaller in diameter thanthe diaphragms which are employed to translate. the lower frequencies.It is also preferable to provide a common sound amplifying horn which isconstructed in such a manner that the low; frequency sound waves will beradiated out of the sound horn with equal efficiency to thesoundwaves ofhigher frequency. Thus the diaphragm 230 for the unit 225 is made.relatively larger in diameter than the diaphragm 130 and accordingly thediaphragm 330 for the electrical unit 25 is made relatively largerindiameter than the diaphragm 230. Also, the throat 231 of the soundamplifying horn 32 is made relatively larger than the throat 131 of theelectrical unit 125 and also the throat331 of the electrical unit 325 ismade relatively larger than the throat 231.

Fig. 2 ofthe drawing shows response curves for the electrical unitdisclosed in Fig. 1. These response curves are plotted between soundresponse and frequency in cycles per second. Curves 1, 2 and 3 show theresponse of the individual units 125, 225 and 325 at different voicefrequencies for constant input of energy. It will be noted that theresonant peak of curve 3 is arranged to be substantially at 50 cycleswhile the peak of curve 2 is positioned at 500 cycles and the peak ofcurve 1 is at 5000 cycles. The resultant response curve for theindividual units taken together is represented by means of curve 4 whichwill be substantially a straight fiat line between the frequencies of 50to 5000 cycles. This means that for a given input of energy into thesystem the response will be substantially the same between thefrequencies of 50 to 5000 cycles per second. The electrical units inreality serve to divide up the voice frequency range into a plurality offrequency bands which are spaced along the voice frequency range and totranslate these frequency bands into sound waves.

Instead of having these electrical units operate separatemechanicalreproducers it is preferable to have them operate a single aperiodicreproducer. Thus, as shown in the modification in Figs. 3 and 4 theelectrical units 125, 225 and 325 actuate a single aperiodic diaphragm.This reproducer is preferably in the form of a conical aperiodicdiaphragm 33 suitably supported at its edges as by a rigid rim 34. Themagnetic unit 129 of the electrical units 125, 225 and 325 in this caseare provided with armatures 35, 36 and 37 which connect with rods 38, 39

and 40. These rods connect to the apex 41 of the conical diaphragm 33and actuate this diaphragm by their joint action. In the operation ofthis system the magnetic units 29 set the armatures 35, 36 and 37 intomechanical vibration and these armatures vibrate the rods 38, 39 and 40longitudinally to actuate jointly the conical diaphragm 33. Since thisdiaphragm is aperiodic'no distortion will be introduced due tomechanical resonance.

The system shown in Fig. 4 is somewhat similar to that shown in Fig. 3but differs in the manner in which the electrical units 125, 225 and.325 are coupled to the, output 12 of the vacuum. tube 11. In this case,the magnetic units 29 are individually connected in series with thecondensers 142, 242 and 342, and are connected in parallel by theconductors 43 and 44. The conductors 43 and 44 are suitably coupled tothe output circuit 12'as by means of an impedance 45. The operation ofthis arrangement is substantially the same as the system shown in Fig.3. The values of the series inductances and capacitances are so selectedthat the electrical units 1, 2 and 3 will attain a value of minimumimpedance at spaced points along the frequency range, as for example, at50 cycles, 500 cycles and 5000 cycles. As in the case of the othersystem, the comb ned effect of the electrical unit upon the diaphragm 33will be to obtain a fiat top characteristic response curve for theentire system.

I claim:

1. In a system of the source of electrical energy modulated at voicefrequencies, means for separating said voice frequencies into aplurality of frequency bands spaced along the voice frequency' range,and translator'means including a single aperiodic diaphragm forconverting said energy into sound waves.

2. In a system of the class described, a source of energy modulated atvoice frequencies, a plurality of magnetic units electrically associatedwith said source, means tor distributing the energy to said units inaccordance with the frequency of the same, and a single aperiodicreproducer mechanically vibrated by energy from said units 3. In asystem of the class described, a source of. electrical energy modulatedat voice frequencies. and means for translating said energy into soundvibrations comprising a plurality of tunedmagnetic units having theirresonant peaks distributed along the voice frequency range, and a singleaperiodic sound reproducer actuated in'accordance with the energy insaid units.

4. in a system of the class described, a

class described, a

source of electrical energy modulated at voice frequencies, a pluralityof separate magnetic telephone units electrically connected with saidsource, a capacitance associated with each unit whereby said units voicefrequencies, means for converting said energy into separate groups ofmechanical vibrations applied to separate mechanical members, a conicalaperiodic'diaphragm, and means for connectingsaid mechanical members tothe center of said diaphragm.

7. In a system of the class described, a

source of electrical energy modulated at voice frequencies, meansfortranslating said energy into mechanical vibrations including aplurality of magnetic units having separate armatures, means associatedwith said units whereby the energy in each unit Will rise to maximum fora certain frequency, the maximum points of the diilerent units beingdistributed along the voice frequency range, a

plurality of rods separately vibrated by said units, and an aperiodicdiaphragm, said rods jointly acting to vibrate said diaphragm from eachof said armatures.

In testimony whereof, I have hereunto set my hand.

rannnarcrr a. KOLSTER.

